Arrangement and automatic control of railway signals for directing only one train tooccupy single track between consecutive passing sidings at any given time



1955 A. R. WHITEHORN 2 7 ARRANGEMENT AND AUTOMATIC CONTROL OF RAILWAYSIGN FOR DIRECTING ONLY ONE TRAIN TO OCCUPY SINGLE TRACK BETWEEN ANYGIVEN TIME CONSECUTIVE PASSING SIDINGS AT Filed March 23,v 1948 3Sheets-Sheet l HIS ATTORNEY Swami VX 1M mw INVENTOR. Arthur H.Wfiiteizorn' v mm mmfiw I RR m k E A a E Q a a A msw E N mm QM 4 N Nu BEN $3 5..

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' II BY E115 A1 TTQZ ZNE FOR DIRECTING ONLY ONE TRAIN TO OCCUPY SINGLETRACK BETWEEN Feb. 22, 1955 A. R. WHITEHORN ARRANGEMENT AND AUTOMATICCONTROL OF RAILWAY SIGNALS CONSECUTIVE PASSING SIDINGS AT ANY GIVEN TIME3 Sheets-Sheet 5 INVENTOR.

Fflzitdzozn Filed March 23, 1948 Art/inn? BY C14 HIS ATTORNEY UnitedStates Patent ARRANGEMENT AND AUTOMATIC CONTROL OF Arthur R. Whitehorn,Pittsburgh, Pa., assignor to Westinghouse Air Brake Company, acorporation of Pennsylvania Application March 23, 1948, Serial N 0.16,447

5 Claims. (Cl. 246-39) My invention relates to a railway signal controlsystem, and particularly to a control system for signals for governingtraific movements in opposite directions over a stretch of single trackrailway.

In a railway signaling system for a stretch of single track railwaywhich is provided with passing sidings spaced along the single track,two pairs of head block signals, each comprising an entering and aleaving signal, are commonly employed for each passing siding forgoverning trafiic movements in opposite directions, and are placed onepair adjacent each end of each passing siding. For stretches of singletrack railway on which trafiic is relatively dense, that is, over whichrelatively many trains move within a given period of time, trainoperation is facilitated by permitting more than one train, moving inthe same direction, to occupy the track between two consecutive sidingsat the same time, although preventing a train which is moving in eitherdirection from entering the stretch of track between two consecutivesidings if the same stretch of track is already-occupied by.

a train moving in the opposite direction. For such train operation, asignal arrangement and control system of the well-known absolutepermissive block type may be employed.

For stretches of single track railway on which trafiic is relativelythin, that is, over which relatively few trains move within a givenperiod of time, it is neither necessary nor important to permit morethan one train moving in either direction to occupy the single trackbetween any two consecutive passing sidings at the same time.

One feature of my invention, therefore, for stretches of single trackrailway on which traffic is relatively thin, but on which train speedsmay be relatively high, is the provision of a signal arrangement whichembodies head block signals similar to those commonly employed exceptthat each of the head block signals displays only two indications, stopand clear. The signal arrangement also embodies an approach signal foreach entering signal, each located a sufficient distance in the rear ofits entering signal to provide double braking distance between eachapproach signal and its entering signal.

Another feature of my invention is the provision of a novel and improvedarrangement of overlapping controls for the leaving head block signalsfor the opposite ends of a stretch of single track railway between twoconsecutive passing sidings.

Another feature of my invention is the provision of track circuitsbetween the two pairs of head block signals at a passing siding in whichthe portion of track between the switch at each end of the passingsiding and the adjacent pair of head block signals is by-passed when theswitch is moved to its reverse position.

Another feature of my invention is the provision of a novel and improvedarrangement for approach controlling a signal by the track circuit forthe second section in the rear of the signal.

Still another feature of my invention is the provision of means forcontrolling an approach signal by current of normal or reverse polarityover a given pair of control conductors, and for controlling the nextleaving signal in the rear of the approach signal by current of reversepolarity only over the same pair of control conductors.

I shall describe one form of apparatus embodying my invention, and shallthen point out the novel'features thereof in claims.

In the accompanying drawings, Figs. la, lb, and 10, when placed end toend in that order, with Fig. 1a on the left, constitute a diagrammaticview showing one form of apparatus embodying my invention, in which astretch of single track railway is provided with passing sidings spacedalong the stretch, and in whichtwo pairs of head block signals areemployed for each passing siding and are placed one pair adjacent eachend of each passing siding, and an approach signal is provided for eachentering signal; and in which the controls for the leaving head blocksignals for opposite ends of the stretch of track between any twoconsecutive passing sidings are overlapped so that the control for eachleaving head block signal extends to the head block signal location atthe remote end of the next passing siding when the switch at the remoteend of the next passing siding is in its normal position, but thecontrol for each leaving head block signal extends only to the switch atthe remote end of the next passing siding, but does not include theswitch, when this switch is in its reverse position; and also in whichthe signal mechanisms and lamps are normally deenergized, and becomeenergized only when a train is approaching.

Similar reference characters refer to similar parts in each of thedrawings.

Referring further to the drawings, a stretch of single track railway isshown, which is provided with a plurality of passing sidings spacedalong the single track. Two such passing sidings, designated by thereference characters X and Y, are shown in the drawings. The ends ofsiding X are connected with the single track railway by switchesdesignated by the reference characters aw and bw, and the ends of sidingY are connected with the single track railway by switches cw and dw.

Rails 1 and 1a of the single track are divided by insulated joints 11 toform sections a-b, b-c, c-d,

de, and e-f. A portion of another section of the single track railway isalso provided to the left of signal I clear position.

18, as shown in the drawings, and a portion of another section is alsoprovided to the right of signal 108, as shown in the drawings. It shouldbe understood that signals 18 and 2S correspond to signals 78 and 8S andthat signals corresponding to signals 68 and 58 would be placed furtherto the left of signal 18. Signals 9S and 108 are counterparts of signals38 and 48. The portion of the system shown in Figsla, lb and 1c isduplicated recurrently to the left and right beyond sidings X and Yrespectively.

An auxiliary insulated joint 12 is also placed in rail 1a of the singletrack adjacent, and in the trailing'direction from, each'of the trackswitches aw, bw, cw, and dw.

Adjacent each end of each of the passing sidings X and Y is a pair ofhead block signals for governing trafiic movements in oppositedirections. Signals 18, 48, 7S, and 108, which govern traflic movementsaway from the passing sidings, are known as leaving signals, whereassignals 28, 38, 8S and 98, which govern traflic movements toward thepassing sidings, are known as entering signals. entering signals, suchas approach signals 58 and 68 shown for entering signals 35 and 33,respectively. Signals 28, 48, 68, 8S and 10S govern traffic movementstoward the right, as shown in the drawings, which I shall assume is theeastbound direction, and signals 18, 38, SS, 78 and 9S govern trafiicmovements in the opposite or westbound direction.

The signals may be of any suitable design, such, for example, as thewell-known searchlight type shown in the drawings, each comprising amechanism, designated by the reference character m, and a lamp,designated by the reference character 1', each of which is preceded by anumerical prefix corresponding to that in the reference character forits signal. The mechanism of each signal is normally in the stopposition, as shown by the solid line at the top of the mast for eachsignal.

Each of the head block signal mechanisms has only one proceed controlposition, shown by the dotted line as the Each of the approach signalshas two An approach signal is provided for each of the proceedpositions, shown by the dotted lines as a caution and a clear position.

Each of the track sections ab and e-f, at the passing sidings, isprovided with two coded track circuits, one for each direction oftraffic movements. The eastbound track circuit for each of thesesections is supplied with current, from a suitable source such as abattery 13 at its east end, coded at a frequency of 120 times per minuteby a code transmitter designated 120CT and includes, at its west end, acode following track relay, designated by the reference character 120CF,which responds to the current coded at the 120 frequency. The westboundtrack circuit for each of these sections is supplied with current, froma suitable source such, for example, as a battery 13, coded at afrequency of 75 times per minute by a code transmitter designated by thereference character 75CT, and includes, at its east end, a codefollowing track relay, designated by the reference character 75CF, whichresponds to the current coded at the 75 frequency.

The circuit for each of the relays 120CF includes the back point of acontact of the adjacent code transmitter 75CT, so that none of the codedcurrent of the 75 frequency from the adjacent battery 13 can passthrough the windings of the relays IZOCF. Similarly, the circuit foreach of the relays 75CF includes the back point of a contact of theadjacent code transmitter 120CT, so that none of the coded current ofthe 120 frequency from the adjacent battery 13 can pass through thewindings of the relays 75CF.

The code transmitters 75CT and 120CT employed at the opposite ends ofsections ab and ef have contacts which are continuously actuated betweentheir picked-up and released positions. These devices are selected sothat their contacts have substantially different rates of operation.Thus, the contacts of the device 120CT are moved to their picked-uppositions 120 times per minute, while the picked-up periods of thecontacts are separated by periods of equal length during which thecontacts occupy their released positions. Similarly, the contacts of thedevice 75CT have 75 picked-up and released periods per minute. As thesedevices operate at substantially different speeds, the contacts do notoperate in synchronism and there are frequently recurring periods duringwhich the contacts of one of the devices are picked {up agd the contactsof the other of the devices are reease During the periods when thecontacts of the code transmitter 120CT for each of the sections ((-12and e-] are picked up while the contacts of the transmitter 75CT for theopposite end of the section are released, impulses of current aresupplied for energizing the relay 120CF for the opposite end of thesection. During the periods when the contacts of the code transmitter75CT for each of the sections rz-b and ef are picked up while thecontacts of the transmitter 120CT for the same section are released,impulses of current are supplied for energizing the relay 75CF for thesame section.

It follows, therefore, that when either of the track sections a-b ande-f is vacant, impulses of energy are supplied from each end of thesection to the track relay at the other end of the section. Theseimpulses are of sufiicient length for controlling relays 75CF and 120CFto effect energization of decoding transformers, each of which isdesignated by the reference character F with a numerical prefix which isthe same as that of the adjacent entering signal, for energizingdecoding track repeater relays, designated by the reference character T?with a numerical prefix which is the same as that of the associateddecoding transformer.

The circuit for each of the relays 75CF and 120CF includes a normalcontact of the adjacent track switch, so that each of these relaysbecomes deenergized when the adjacent switch is moved away from itsnormal posilOIl.

A switch repeater relay is provided for each switch, and 1s deslgnatedby the reference character P with a prefix which is the same as theprefix in the reference character for its switch. Each of these switchrepeater relays is controlled in conjunction with its switch by acontact which is normally closed when its switch is in the normalposition and becomes opened when its switch is moved to the reverseposition, so that each switch repeater relay becomes deenergized whenits switch is moved away from the normal position.

A circuit path is included in each of the track circuits for sections aband ef, connected around each of the insulated joints 12 with the trackrail 1a in which the joint 12 is located, through a front contact of theswitch repeater relay for the adjacent switch. When a switch is movedaway from its normal position, a bypass is completed, through a backpoint of a contact of the switch repeater relay, around a portion of thetrack rail 1a in which the adjacent insulated joint 12 is located.

The portion of the track rail thus by-passed extends between theadjacent insulated joint 12 and the adjacent end of the track section,so that the code following relay CF or IZOCF for the opposite end of thesection will not be affected by a train moving over the switch in itsreverse position.

Each of the track sections b-c and de, and also the first section westof signal 18 and the first section east of signal 105, is provided witha polarized coded track circuit, one end of which is supplied withcurrent of normal or reverse polarity coded at a frequency of 75 timesper minute by a code transmitter 75CT, and the opposite end of whichincludes two polar biased code following track relays, designated by thereference characters TRN and TRR with a distinguishing numerical prefix,connected in series opposition across the rails of the section. Therelay designated by the reference character TRN responds by operatingits contacts between front and back points only when the track circuitis energized by coded current of normal polarity, and similarly therelay desig nated by the reference character TRR responds by operatingits contacts between front and back points only when the track circuitis energized by coded current of reverse polarity.

The relays TRN and TRR control decoding track repeater relays designatedby the reference characters DP, TNP and TRP, preceded by a numericalprefix which is the same as that of the associated relays TRN and TRR.Each of the relays DP is made slow releasing by an asymmetric unit t,which may be of the well-known copper oxide rectifier type, connectedwith its high resistance direction in multiple with the winding of therelay DP. Each of the relays TNP and TRP is also made slow releasing bya resistor r and a condenser u connected, in series with each other, inmultiple with its winding.

Section 0-11 is provided with a center-fed coded track circuit which issupplied with current coded at the frequency of 75 times per minute by acode transmitter 75CT, and which includes a code following track relaySTR connected across one end of the section, and a second code followingtrack relay, designated by the reference character 6TR, connected acrossthe opposite end of the section. Each of the relays 5TR and 6TR controlsa track repeater relay through a decoding transformer F.

The mechanism In and lamp i for each signal are normally deenergized,and become energized when a train approaches their signal in thedirection of trafiie movements governed by their signal.

Having described, in general, the arrangement and control of theapparatus shown by the accompanying drawings, I shall now describe, indetail, its operation.

As shown by the drawings, all parts of the apparatus are in their normalcondition, that is, switches aw, bw, cw, and dw are in their normalposition; each signal mechanism m is deenergized, and each signal lamp1' is unlighted; each of the code transmitters 75CT and CT is energized;switch repeater relays 0P, bP, 0P, and dP, track relays ITRN, 120CF,75CF, 4TRN, STR, 6TR, 7TRN, and IOTRN, and decoding track repeaterrelays IDP, lTNP, 2TP, 3TP, 4DP, 4TNP, 5T1, 6TP, 7DP, 7TNP, 8TP, 9TP,10DP, and 10TNP are in the picked-up condition; and track relays lTRR,4TRR, 7TRR and 10TRR, and decoding track repeater relays lTRP, 4TRP,7TRP and 10TRP are deenergized.

The circuit by which relay aP is energized passes from terminal B of asuitable source of current, through contact 15 operated in conjunctionwith switch aw, and the winding of relay al to terminal N of the samesource of current. Each of the relays bl, cP and d? is energized by asimilar circuit.

Each of the code transmitters 75CT and 120CT is constantly connectedacross terminals B and N, so that each of the code transmitters isconstantly moving its contacts between closed and open positions at thefrequency of 75 or 120 times per minute for which it is designed.

The contacts of each of the code transmitters 75CT are thereforerepeatedly moved alternately to their front and back positions 75 timesper minute. Similarly, the contacts of each of the code transmitters120CT are repeatedly moved alternately to their front and back positions120 times per minute. The circuit by which relay 120CF for section ab isperiodically energized passes from a suitable source of current, such asa battery 13, through the front point of contact 16 of relay bP, rail 1aof section ab, contact 17 of relay bP, rail 1a of section ab, contact 17of relay aP, rail 1a of section a-b, winding of relay 120CF, contact 18operated in conjunction with switch aw, back point of contact 19 of acode transmitter 75CT, rail 1 of section a.b, and the front point ofcontact 20 of a code transmitter 120CT, back to battery 13. The circuitby which relay 75CF for section a--b is periodically energized passesfrom battery 13 at the west end of section ab, through the front pointof contact 16 of relay aP, rail 1a of section a-b, front point ofcontact 17 of relay aP, rail 1a of section a-b, front point of contact17 of relay bP, rail in of section a-b, contact 18 operated inconjunction with switch bw, winding of relay 75CF, back point of contact20 of code transmitter 1'20CT, rail 1 of section ab, and the front pointof contact 19 of code transmitter 75CT, back to battery 13. Relays 120CFand 75CF for section e-f are energized by circuits which are similar tothe circuits just traced for relays 120CF and 75CF, respectively, forsection ab.

With relay 120CF for the west end of section ab repeatedly moving itscontact 21 between front and back points, primary winding y of decodingtransformer 2F is repeatedly energized, alternately in oppositedirections, by current passing from terminal B through the front andback points of contact21 of relay 120CF, and upper and lower portions,respectively, as shown in the drawing, of winding y, to terminal N.Alternating current is thereby generated in secondary winding n oftransformer 2F, and is rectified by the front and back points of contact22 of relay 120CF for energizing track repeater relay ZTP. Decodingtransformer 3F and track repeater relay 3T? are controlled by relay 75CFat the east end of section a-b similarily to the manner described inwhich transformer 2F and relay 2TP are controlled by relay 12iiCF at thewest end of section ab. Transformers 8F and 9F and relays 8TP and 9TPfor section ef are controlled similarly to the correspondingtransformers and relays for section a.b as just described.

Relay 4TRN for section b-c is energized by current of normal polarity ina circuit passing from battery 13 at the east end of section b-c,through the front point of contact 23 of relay STP, contact 24 of codetransmitter 75CT, rail 1a of section b-c, windings of relays 4TRR and4TRN in series opposition, rail 1 of section b-c, and the front point ofcontact 25 of relay STP back to battery 13. Relay 4TRN responds to thecoded current of normal polarity, thus supplied to section b-c, byrepeatedly moving its contact 26 between its front and back points,whereas contact 28 of relay 4TRR remains constantly closed at its backpoint.

During the periods when contact 26 of relay 4TRN is closed at its backpoint, relay 4DP is energized by current passing from terminal B,through the back point of contact 26 of relay 4TRN, back point ofcontact 28 of relay 4TRR, and the winding of relay 4DP in multiple withthe high resistance direction of asymmetric unit I, to terminal N.During the periods when contact 26 of relay 4TRN is closed at its frontpoint, relay 4TNP is energized by current passing from terminal B,through the front point of contact 26 of relay 4TRN, contact 27 of relay4DP, and the winding of relay 4TNP in multiple with a path through aresistor r and a condenser u to terminal N. Relays lTRN, 7TRN, and IGTRNare energized similarly to relay 4TRN as previously described. RelaysIDP, 7D? and DI are also energized similarly to relay 4DP, and relayslTNP, 7TNP and itlTNP are energized similarly to relay 4TNP.

Relay STR is energized by current supplied by a battery13 at anintermediate point of section b-c, through contact 54 of a codetransmitter 75CT. Relay STR, being of the code following type, thereforerepeatedly moves its contacts 21 and 22 between their front and backpoints, and thereby effects energization of relay STP from transformer5F. Relays 6TR and 6TP are 6 energized similarly to relays 5TR and STP,respectively, as just described.

I shall assume that, with apparatus embodying my invention, as shown inthe drawings, thus in the normal condition, an eastbound trainapproaches signal 28 and deenergizes relay ITRN, which in turndeenergizes relay iTNP. With relay ITNP deenergized, mechanism 2m ofsignal 28 becomes energized by current passing from a suitable source,such as a battery 14 shown adjacent the mechanism 3m for signal 38,through the front point of contact 30 of relay 4TNP, contact 31 of relay3TP,

control conductor 32, contact 33 of relay 2TP, back point of contact 34of relay lTNP, mechanism 2m, back point of contact 35 of relay lTNP,control conductor 35, and the front point of contact 37 of relay 4TNP,back to battery 14. At the same time, lamp 21' of signal 28 becomeslighted by current passing from terminal EB of a suitable source oflighting current, through contact 38 of relay 1TNP, and lamp 2i toterminal EN of the same source of lighting current. With mechanism 2111thus energized and lamp 2i lighted, signal 28 displays the clear proceedindication.

The eastbound train, upon passing signal 28 into section ab, shunts bothtrack circuits for this section, thereby deenergizing both of the trackrelays 75CF and 126CF for section a-b. With relay 120CF deenergized,relay 2T1 becomes deenergized, and therefore the circuit for mechanism2m of signal 25 becomes opened at contact 33 of relay ZTP, causingsignal 25 to indicate stop. Signal 23 will continue to display the stopindication as long as lamp 21' remains lighted because of thedeenergization of relay ITRN by the train.

With relay 75CF deenergized, relay 3TP is also deenergized, so thatmechanism 4m of signal 48 is now energized by current passing frombattery 14 adjacent signal 88, through the back point of contact 40operated in conjunction with mechanism 8m of signal 88, front point ofcontact 41 of relay 8TP, front point of contact 42 of relay 6TP, frontpoint of contact 43 of relay 5TP, control conductor 44, back point ofcontact 45 of relay 3TP, mechanism 4m, back point of contact 46 of relay3TP, contact 47 of relay 4TNP, control conductor 49, front point ofcontact 50 of relay STP, front point of contact 51 of relay 6TP, contact47 of relay 7TNP, front point of contact 52 of relay STP, and the backpoint of contact 53 of mechanism 8m, back to battery 14. With relay 3T1deenergized, lamp 4i of signal 48 is lighted by a circuit passing fromterminal EB, through contact 39 of relay 3T1, and lamp 41' of signal 48to terminal EN. With mechanism 4m energized and lamp 4i lighted, signal45 now displays the clear proceed indication.

When the train enters section bc, deenergizing relay 4TRN, relay iTNl,in turn, becomes deenergized, and therefore its contact 47 opens thecircuit traced for mechanism 4m, causing signal 45 to now display thestop indication. Signal 48 will then continue to display the stopindication as long as lamp 4i is lighted because of relay 3TP beingdeenergized by the train on section a-b.

When the train enters section c-d, relay STR becomes deenergized,causing relay STP in turn to also be deenergized. The train, uponentering section cd, also deenergizes relay 6TR, causing relay 6TP to inturn be deenergized. With relay 6TP deenergized, mechanism 6m of signalbecomes energized by current of reverse polarity passing from battery 14adjacent relay STP in Fig. 10, through the back point of contact 40operated in conjunction with signal mechanism 8m, front point of contact41 of relay STP, back point of contact 42 of relay 6TP, mechanism 6m,back point of contact 51 of relay 6TP. contact 47 of relay '7TNP, frontpoint of. contact 52 of relay 8T5, and the back point of contact 53operated in conjunction with signal 8m back to battery 14. At the sametime, lamp 6i of signal 68 becomes lighted by a circuit which is similarto the circuit shown for lamp 5i of signal 58. Signal 65, therefore,displays the caution indication.

With relay 6TP deenergized, a circuit is completed for energizing relays7TRN and 7TRR by current of reverse polarity, this circuit passing frombattery 13 adjacent signal mechanism 6M, through the back point ofcontact 25 of relay 6TP, rail 1 of section d-e, windings of relays 7TRRand 7TRN in series, rail 1a of section de, contact 24 of codetransmitter CT, and the back point of contact 23 of relay 6TP back tobattery 13. With relays 7TRN and 7TRR now energized by current ofreverse polarity, relay 7TRR responds by repeatedly moving its contact28 between its front and back points, and contact 26 of relay 7TRNceases to move between its front and back points and remains closed atits back point. Relay 7TNP is therefore now deenergized, and relay 7TRPbecomes energized by its circuit passing from terminal B, through theback point of contact 26 of relay 7TRN, front point of contact 28 ofrelay 'YTRR, contact 29 of relay 7DP, and the winding of relay 7TRP inmultiple with a path through a resistor r in series with a condenser 11,to terminal N.

A second circuit is now completed for mechanism 511:, which is the sameas the circuit previously traced except that it includes contact 48 ofrelay '7TRP instead of contact 47 of relay 7TNP.

With relay 7TNP deenergized, mechanism 8m of signal SS becomes energizedby its circuit passing from battery 14 adjacent signal 108, through thefront point of contact 30 of relay IOTNP, contact 31 of relay 9T1control conductor 32, contact 33 of relay STP, back point of contact 34of relay 7TNP, mechanism 8m, back point of contact 35 of relay 7TNP,control conductor 36, and the front point of contact 37 of relay 10TNP,back to battery 14. With relay 7TNP deenergized, lamp 8:" of signal 88is lighted by a circuit passing from terminal EB, through contact 38 ofrelay 7TNP, and lamp 81' to terminal EN. With mechanism 8111 thusenergized and lamp 8i lighted, signal 88 will now display the clearproceed indication.

When mechanism 8112 is moved to its clear position, contacts 40 and 53operated in conjunction with mechanism 8m become closed at their frontpoints, so that now mechanism 6111 becomes energized by current ofnormal polarity in a circuit which is the same as the circuit previouslytraced for this mechanism except that it includes the front points ofcontacts 4t) and 53 of signal mechanism Sm instead of the back points ofthese contacts. Signal 65 therefore now changes from the caution to theclear proceed indication.

When the train enters section d-e. relay TFRR becomes deenergized, sothat relay 7TRP, in turn, also becomes deenergized. Mechanism 6m ofsignal 65 is then deenergized by the opening of contact 48 of relay7TRP, so that signal 65 changes from the clear proceed to the stopindication.

When the train enters section e-f, the operation of the apparatus atpassing siding Y is similar to that previously described for theapparatus at siding X when the train entered section ab.

I shall now assume that all parts of the apparatus are again in thenormal condition, and that an eastbound train passes signal 28 ontosection nb, causing signal 48 to display the clear proceed indication,as previously described. I shall assume further that a westbound trainapproaches signal 98, deenergizing relay IOTRN, which in turndeenergizes relay IOTNP, so that mechanism 9m becomes energized by acircuit which is similar to the circuit previously traced for energizingmechanism 8m when an eastbound train approached signal 88. Lamp 91' forsignal 98 becomes lighted by a circuit which is similar to the circuitpreviously traced for lamp 8: of signal 88.

I shall also assume further that the westbound train passes signal 98before the eastbound train reaches signal 48, so that relays 75CF and120CF for section e-J become deenergized. With this relay 75CFdeenergized, relay 9TP also becomes deenergized, causing mechanism 9m inturn to also be deenergized, so that signal 98 will now indicate stop.

With relay 120CF for section deenergized, relay STP is in turndeenergized, but mechanism 7111 does not become energized because relaySTP at section a-b has already been deenergized by the eastbound trainon section n-b. With relay 8TP deenergized, mechanism 4/12 for signal 43becomes deenergized. Signal 45 will therefore display the stopindication for the eastbound train, and signal 78 Will display the stopindication for the westbound train.

One of the trains will then take a passing siding allowing the other toclear on the main track in accordance with established priority.

I shall next assume that all parts of the apparatus are again returnedto the normal condition, and that a westbound train approaches signal 95while an eastbound train is approaching signal 48 on section ab. I shall8 assume further that the westbound train stops, and that a trainmanreverses switch dw at the east end of siding Y for the westbound trainto move onto siding Y so that the eastbound train can pass the westboundtrain at this siding.

When switch dw is moved away from its normal position, contact 15, whichis operated in conjunction with this switch, opens the circuit for relay(11, causing relay (1P to become deenergized. Contact 18, also operatedin conjunction with switch dw, becomes opened when switch dw is movedaway from its normal position, thereby causin g relay 75CF at the eastend of section e-f to become deenergized which in turn causes relay 9TPto become deenergized.

With relay [1P deenergized, a portion of the rail 1a of section efbetween insulated joints 12 adjacent switch dw and signal 98 isby-passed in a track circuit which includes relay 120CF for section e-f.Relay 120CF is therefore now energized by current passing from battery13 adjacent switch a'w, through the back point of contact 16 of relaydP, rail 1a of section ef, front point of contact 17 of relay cP, rail1a of section ef, winding of relay 120CF, contact 18 operated inconjunction with switch cw, back point of contact 19 of code transmitter75CT, rail 1 of section ef, and the front point of contact 20 of codetransmitter 120CT, back to battery 13.

Relay 8TP will therefore also be energized, and signal mechanism 4m willbe energized, as previously described, because of the eastbound train onsection a-b. Signal 48 will therefore display the clear proceedindication for the eastbound train.

It follows that the presence of the westbound train on section ef,moving onto siding Y over switch dw, does not cause signal 48 toindicate stop, and so the eastbound train may proceed past signal 48.

When the westbound train has moved off of section e-f onto siding Y,relay 75CF for section ef will still be deenergized while switch dw isin its reverse position causing its contact 18 to be open. With relay75CF for section ef deenergized, relay 9TP will be deenergized, and sosignal 98 cannot clear for a following train, and signal 88 cannot clearfor the eastbound train. Therefore, if, while switch dw is still in itsreverse position, the eastbound train enters section c--d, signal 88cannot clear on account of relay 9T1 being deenergized, mechanism SMremains in its deenergized position, contacts 40 and 53 remain in theposition as shown on Fig. 1c in which current of reverse polarity isapplied to mechanism 6M and therefore signal 65 will display the cautionindication for the eastbound train.

I shall now assume that all parts of the apparatus are again in thenormal condition, and that an eastbound train passes signals 28 and 48onto section b-c, and that a westbound train approaches signal 98,causing signal to clear as previously described. I shall assume furtherthat the eastbound train enters section cd before the westbound trainreaches signal 98. With the eastbound train on section cd, relay 6TPwill be deenergized, so that relay 7TNP will also be deenergized andrelay 7TRP will be energized as previously described.

With relay 10TNP deenergized because of the westbound train approachingsignal 95, signal 88 cannot clear for the eastbound train, and thereforesignal 68 will display the caution indication. With relay 7TNPdeenergized because of the eastbound train, signal 98 will be controlledto indicate stop for the westbound train, while the eastbound train willreceive a stop indication from signal 88.

Assuming that the westbound train had orders to take the passing sidingupon meeting the eastbound train it would have been traveling inanticipation of stopping prior to reaching switch dw and could nowproceed into the siding under flag protection. However, in any event,the signal indications would be such as to stop the trains before acollision would occur.

From the foregoing description, it follows that, with all switches inthe normal position, the control for each leaving head block signal isoverlapped to the entering signal at the remote end of the next passingsiding in advance, that is, with all switches in the normal position,the control circuit for leaving head block signal 48 extends to enteringsignal 98 at the opposite end of siding Y, and the control circuit forleaving head block signal 78 extends to entering signal 28 at theopposite end of siding X. v I

When switch dw at the east end of siding Y is reversed, the control forsignal 48 extends only to the insulated joint 12 adjacent switch dw, andsimilarly, when switch aw is reversed, at the west end of siding X, thecontrol for signal 78 extends only to the insulated joint 12 adjacentswitch aw.

It also follows, from the foregoing description, that the control foreach entering head block signal is overlapped to the approach signal forthe next entering signal in advance which governs traflic movements inthe same direction, so that the control for signal 98 extends to signal58, and the control for signal 85 extends to the approach signal for thenext eastbound entering signal similarly to the arrangement shown forcontrolling signal 28 to signal 68.

I have described the operation of the apparatus for only a few typicaltraflic movements. It is believed that, in view of those descriptions,the operation of the apparatus for any other possible trafiic movementcan be readily traced on the accompanying drawings.

Although I have herein shown and described only one form of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my in vention.

Having thus described my invention, what I claim is:

l. A signal location and control arrangement for a stretch of singletrack railway which is provided with passing sidings spaced along saidstretch, comprising in combination, two pairs of head block signals foreach passing siding each pair comprising an entering and a leavingsignal located one pair adjacent each end of each passing siding, meanscontrolled by traffic conditions for controlling each entering signalfor each siding to display a stop or a proceed indication according assaid stretch of track is occupied or unoccupied between that enteringsignal and a point beyond the opposing entering signal for the nextsiding, a track switch located adjacent each end of each passing siding,means controlled by trafiic conditions for controlling each leavingsignal to display a stop or a proceed indication according as saidstretch of track is occupied or unoccupied between each leaving signaland the opposing entering signal for the next siding if the track switchadjacent said opposing entering signal at the next siding is in itsnormal position, a short insulated track section for each track switch,said short insulated track section including the portions of saidstretch of track and of the siding lying on each side of the associatedtrack switch, and means for eliminating from the control of each leavingsignal the traflic conditions for the short insulated track section ofsaid stretch of track between the opposing entering signal at the nextsiding and said adjacent track switch during the times when saidadjacent track switch is in its reverse position.

2. In combination, a section of railway track including a switch, aninsulated joint in one rail of said track section, a switch repeaterrelay controlled in conjunction with said switch to be energized only ifsaid switch is in its normal position, a circuit path including a frontcontact of said switch repeater relay connected with said one railaround said insulated joint, a track circuit including a suitable sourceof current connected across the rails of one end of said section througha front contact of said switch repeater relay and including a trackrelay connected across the rails of the opposite end of said section,means including a back contact of said switch repeater relay forconnecting said source of current between the other rail of said sectionand said one rail on the opposite side of said insulated joint from saidone end of said section, and traffic governing means controlled by saidtrack relay.

3. In combination, a section of railway track including two switches oneadjacent each end of said section, a source of current and a track relayconnected across a given end of said section through contact meansclosed only if the adjacent switch is in its normal position, anauxiliary insulated joint in one of the rails of said section adjacenteach of said switches, means including a contact which is closed only ifthe switch adjacent said given end of said section is in its reverseposition for connecting said source of current between the opposite railand said one rail on the opposite side of the adjacent auxiliaryinsulated joint from said given end of said section, a second source ofcurrent and a second track relay connected across the opposite end ofsaid section through contact means closed only if the switch adjacentsaid opposite end of said section is in its normal position, meansincluding a contact which is closed only if said second switch is in itsreverse position for connecting said second source of current betweenthe opposite rail and said one rail on the opposite side of the adjacentauxiliary insulated joint from said opposite end of said section, andtraffic governing means controlled by said track relays.

4. In combination, a section of railway track including two switches oneadjacent each end of said section, a track circuit including a source ofcurrent connected through a front contact of a given coding deviceacross a given end of said section and including a track relay connectedthrough a back contact of a second coding device across the opposite endof said section, means controlled in conjunction with the switchadjacent said given end of said section for by-passing a portion of saidsection in said track circuit when the switch is moved to its reverseposition, a second track circuit including a second source of currentconnected through a front contact of said second coding device acrosssaid opposite end of said section and including a second track relayconnected through a back contact of said first coding device across saidgiven end of said section, means controlled in conjunction with theswitch adjacent said opposite end of said section for by-passing aportion of said section in said second track circuit when this switch ismoved to its reverse position, and signal apparatus controlled by saidtrack relays.

5. In a signal location and control arrangement for a stretch of singletrack railway which is provided with passing sidings spaced along saidstretch, and wherein there is provided a pair of head block signals foreach end of each passing siding, each pair comprising an entering and aleaving signal and each of said entering and leaving signals controlledby trafiic conditions to display only a stop indication or a clearindication, the combination of a first entering signal for one of thepassing sidings, an approach signal located a sufficient distance in therear of said entering signal to provide double braking distance betweenthe approach signal and the first entering signal, an approach tracksection in the rear of said approach signal, a track circuit for saidapproach track section which is normally energized but which becomesdeenergized when a train approaches said approach signal through saidapproach track section, a track circuit for the portion of said trackbetween said approach signal and its associated entering signal, saidtrack circuit being normally energized by current of normal polarity butbecoming energized by current of reverse polarity in response to a trainentering said approach track section, a second entering signal for thenext passing siding in advance, an approach signal for said secondentering signal, means controlled by trafiic conditions in advance ofthe approach signal for the first entering signal up to the approachsignal for the second entering signal and including said track circuitfor said portion of said track upon becoming energized by current ofreverse polarity for controlling said first entering signal to display aproceed indication or a stop indication, a pair of head block signals atthe remote end of said one of the passing siding-s and means, includingsaid track circuit for said approach track section upon becomingdeenergized, for controlling the approach signal associated with saidfirst entering signal to display a caution or a clear indicationaccording as said first entering signal is controlled to display a stopor proceed indication, and further means to cause the approach signalassociated with the first entering signal to display a stop indicationin response to the presence of a train on said single track at any pointbetween the approach signal and the pair of head block signals at theremote end of said one of the passing sidings.

References Cited in the file of this patent UNITED STATES PATENTS531,284 Wilson Dec. 18, 1894 1,194,116 Abernethy Aug. 8, 1916 (Otherreferences on following page) 11 Wight Feb. 18, Wight Apr. 8, Wight Apr.8, Wight Apr. 8, Spray Jan. 27, Pfiasterer Oct. 18, Pflasterer May 13,

12 Thompson May 19, 1942 Kemmerer July 14, 1942 Young et a1 Sept. 29,1942 Scheg Jan. 9, 1945 Langdon Jan. 1, 1946 Nicholson Feb. 8, 1949Fereday Dec. 23, 1952

